Hydraulically operated working machine

ABSTRACT

Hydraulically operated working machine such as a puncher provided with a piston retracting mechanism including a high power piston retracting element or elements such as an urethane body or bodies or a washer spring or springs and disposed outside the machine main parts confining a piston chamber, all the auxiliary elements such as a piston shifting mechanism being incorporated within the machine main parts for convenience in use and transportation of the machine.

States atent [191 tsuhashi et a1; 5] Dec. 9, 1975 [5 HYDRAULICALLY OPERATED WORKING 3,126,630 3/1964 Catlin (it al. 30/358 MACHINE [75] Inventors: Shigeru Mitsuhashi; Kyoichi P rzmary Examiner-A1 Lawrence Smith g fw fi l fzzgi fifi Assistant ExaminerJ. T. Zatarga am c m s Masuna Attorney, Agent, or FirmOstrolenk, Faber, Gerb & Kowada; Yasuo Kazama, all of Soft-en Tokyo, Japan [73] Assignee: Nitto Kohki Co., Ltd., Tokyo, Japan [22] Filed: July 1, 1974 [57] ABSTRACT [21] Appl. No.: 484,552

Hydraulically operated working machine such as a puncher provided with a piston retracting mechanism [30] Forelgn Apphcauon Pnonty Dam including a high power piston retracting element or Aug. 4,1973 Japan .1 48-91668 lements such as an urethane body 01' bodies or a washer spring or springs and disposed outside the ma- [52] U-S. 30/358 chin main parts confining a piston chamber all the [5]] lift. Q1. B26F a iliary elements uch as a piston mechanism Fleld of Search 361, 180, being incorporated within the machine main parts for 30/228 convenience in use and transportation of the machine.

[56] References Cited 7 C 13 F UNITED STATES PATENTS lalms Drawmg gums 3,008,234 11/1961 Mattera 30/358 X U.S. Patent Dec. 9 1975 Sheet 1 of 6 3,924,330

US. Patent Dec. 9 1975 Sheet 2 of6 3,924,330

US. Patent Dec. 9 1975 Sheet 3 of6 3,924,330

FIGS

FIG.7

US. Patent Dec.91975 Sheet4 of6 3,924,330

FIGB

US. Patent Dec. 9 1975 Sheet 5 of6 3,924,330

US. Patent Dec. 9 1975 Sheet 6 of6 3,924,330

HYDRAULICALLY OPERATED WORKING MACHINE The present invention relates to a hydraulically operated working machine, and more particularly relates to an improvement in the structure of an hydraulically operated working machine of a single-acting piston type such as a puncher or the like.

In the case of conventional hydraulically operated working machines of a single-acting piston type such as punchers, the forward stroke of the piston mechanism is in general actuated by oil pressure while the return stroke of same is actuated by repulsion of a spring element or elements disposed within the machine main parts. In other words, the piston retracting mechanism is in general incorporated within the machine main parts which confine a piston chamber.

Due to this incorporation of the piston retracting mechanism within the machine main parts, demand for a strong piston retracting force naturally requires enlarged repulsion of the piston retracting mechanism. This inevitably results in a correspondingly increased oil pressure exerted on the piston mechanism and enlarged size of the spring element or elements. Therefore, in order to obtain a strong piston retracting force, it is necessary to provide the working machine with a large, stalwart and stout structure.

However, this need for the stalwart machine structure does not meet the recently growing general demand for compact working machines for convenience in use and transportation of same. Especially in the case of such working machines as punchers, handy and compact machine structures are preferred by their users.

Employment of a spring element or elements of rather small size, i.e. small repulsion, as the piston retracting element in a puncher, for example, forces the users to provide relatively large clearances between the puncher and the hole to be punched. It is experienced generally that such large clearance between the punch and the hole causes production of sharp irritating noises at the time of the punching operation and low quality surface condition of the hole wall after the punching. in addition, spring elements of the relatively small size will fatigue very easily and can hardly withstand long use.

Therefore, in order to enhance the utility of the hydraulically operated working machine of a single-acting piston type it is strongly required to provide the machine with a high power piston retracting mechanism on one hand and a relatively handy, compact and light structure on the other hand.

Even aside from the viewpoint of the machine size, incorporation of the piston retracting mechanism within the machine main parts makes maintenance and component replacement operations very troublesome and difficult. As already mentioned, the piston retracting mechanism endures repeated compression under severe conditions and is liable to fatigue which leads to destruction and hence loss of its expected function. So, it is preferable that the piston retracting mechanism should be so combined with the machine structure that the same can be ery easily disassembled for replacement from the machine structure.

It is further desired by the users that auxiliary elements of the machine, e.g. the mechanism for admission and discharge of pressured fluid into and out of the piston chamber and electric arrangement for shifting of 2 the piston strokes, should not be exposed on the outer side of the machine so that the machine can be easily used and transported.

The primary object of the present invention is to provide an improved hydraulically operated working machine such as a puncher provided with highly enhanced piston retracting force together with a relatively handy, compact and light structure.

Another object of the present invention is to provide an improved hydraulically operated working machine such as a puncher whose piston retracting mechanism can be replaced very easily by reduced trouble in the maintenance work.

Another object of the present invention is to provide an improved hydraulically operated working machine such as a puncher having an outer design conveniently suited for handling and transportation of same.

A further object of the present invention is to provide an improved hydraulically operated working machine such as a puncher, which, when used as a puncher, is capable of forming holes through work pieces with minimized clearance, enhancing the accuracy in hole formation, advantageously limiting the production of irritating, sharp noises at the time of the punching operation and providing the punched holes with smooth and fine wall surfaces.

In order to attain the above-described objects of the present invention, the hydraulically operated working machine of the present invention comprises a piston retracting mechanism attached to the machine at a position outside the machine main parts confining a piston chamber, in engagement with an extension of the piston mechanism, the piston retracting mechanism including as its major part, one or more high power retracting elements such as urethane bodies or superimposed washer springs and auxiliary mechanisms, e.g. a mechanism for admission and discharge of the pressured operating fluid into and out of the piston chamber, are all incorporated within the machine main parts. The machine is preferably provided with a further mechanism for automatically shifting the piston strokes.

Further features and advantages of the present invention will be made clearer from the following description, reference being made to the embodiments shown in the accompanying drawings in which;

FIG. 1 is a top plan view of the hydraulically operated working machine according to one aspect of the present invention,

FIG. 2 is a side plan view of the hydraulically operated working machine shown in FIG. 1,

FIG. 3 is a side plan view, partly in section, of the first embodiment of the hydraulically operated working machine shown in FIG. 2;,

FIG. 4 is a sectional plan view taken along the line IV IV in FIG. 3,

FIG. 5 is a sectional plan view taken along the line V V in FIG. 3,

FIG. 6 is a fragmentary sectional plan view of the piston shifting mechanism and its related parts used in the hydraulically operated working machine shown in FIG.

FIG. '7 is a fragmentary sectional plan view of the main handle possessed by the hydraulically operated working machine shown in FIG. 3,

FIG. 8 is a circuit diagram usable for the hydraulically operated working machine according to one aspect of the present invention,

FIG. 9 is a fragmentary sectional plan view of a modification of the hydraulically operated working machine shown in FIG. 3,

FIG. is a side plan view, partly in section, of the second embodiment of the hydraulically operated working machine shown in FIG. 2,

FIG. 11 is a perspective plan view of a guide cylinder usable for the hydraulically operated working machine shown in FIG. 10,

FIG. 12 is a sectional plan view taken along the line XII XII in FIG. 13, and

FIG. 13 is a side plan view, partly in section, of the hydraulically operated working machine shown in FIG. 10 with the piston retracting mechanism in a compressed disposition.

The first embodiment of the present invention is shown in FIGS. 1 through 3, in which the hydraulically operated working machine of the present invention includes a C-shaped main frame 1, a cap 2 disposed to the upperside of the main frame 1 and accommodating an interior mounted piston mechanism which will be later explained in detail, a piston retracting mechanism 3 mounted to the upperside of the cap 2, a main handle 4 disposed sideways to the main frame 1, an auxiliary handle 6 disposed also sideways to the main frame 1, a piston mechanism 7 accommodated within the main frame 1, the cap 2 providing for an axial reciprocation, and a work part 8 disposed to the lower end of the piston mechanism 7.

As is clearly seen from FIG. 2, the main frame 1 has a C-shaped side view profile and is composed of an upper jaw 11, a lower jaw 12 and a connecting arm 13 for integrally connecting the two jaws l1 and 12. The upper half of the upper jaw 11 is internally threaded and the lower half of the same is provided with a through hole 14 for accommodating the work part 8. The lower jaw 12 is provided with a seat for a die 16 and a vertical through hole 17 in communication to with the center hole of the die 16. The through hole 14 of the upper jaw 11, the die 16 and the through hole 17 of the lower jaw 12 are in a coaxial alignment. In the case of the illustrated embodiment, the die 16 held by the lower jaw 12 is suited for the punching operation and, therefore, the through hole 17 of the lower jaw 12 is used for discharging punched pieces of work pieces to be operated upon.

The cap 2 is composed of an upper flange part 21 and a piston cylinder 22 formed downwards integrally of the upper flange part 21, the upper flange part 21 defining the upper end of a piston chamber 23. The piston cylinder 22 of the cap 2 is externally threaded for a threaded engagement with the internally threaded upper part of the main frame upper jaw 11. In communication with the piston chamber 23, a pressure fluid passage 24 is formed in the upper flange part 21 of cap 2. A center through-hole is formed vertically in the upper flange part 21 of cap 2 in order to allow for reciprocal sliding of the later described piston rod of the piston mechanism 7.

The piston retracting mechanism 3 forms the main part of the present invention and is mounted to the upperside of the cap upper flange part 21. In other words, the piston retracting mechanism 3 is located quite outside the main body of the working machine in the present invention. This piston retracting mechanism 3 is comprised of a hollow cover 31 fixed to the cap upper flange part 2 l and a retracting element 32 made of urethane rubber and encased within the cover 31. In the case of the illustrated embodiment, this retracting element 32 is divided into two pieces by a later described separator plate. The retracting element 32 is placed on the upper face of the cap upper flange part 21 in an idle engagement with the later described piston mechanism 7.

The piston mechanism 7 includes a piston plunger 73 slidably accommodated within the piston chamber 23, an upper piston rod 72 and a lower piston rod 74, the three parts being formed integrally of each other. The upper piston rod 72 extends upwardly into the cover 31 through the center through hole of the cap upper flange part 21 and the urethane rubber retracting element 32. A flange 71 is fixed to the top end of the upper piston rod 72 via a set bolt 76 with its underface in direct contact with the upper face of the retracting element 32. In the case of the illustrated embodiment, a horizontal separator plate 77 is fixed substantially at a midway point of the upper piston rod 72 in order to divide the retracting element 32 into two pieces. The lower piston rod 74 is suited for holding the later described work part 8.

In the case of the illustrated embodiment, the work part 8 is designed so as to be suitable for punching operations and is provided with a punch 82 which coacts with the die 16 held by the main frame lower jaw 12. An externally threaded fixer ring 83 is in threaded engagement with the internally threaded bottom hollow portion of the lower piston rod 74 in order to secure the punch 82 to the bottom end of the lower piston rod 74. In order to slidably guide the reciprocation of the lower piston rod 74, a guide sleeve 81 is fixedly fitted into the through hole 14 of the main frame upper jaw 11. At a position slightly below the guide sleeve 81, a stripper 84 is threaded at its upper portion to threadedly engage the internally threaded lower portion of the through hole 14 while spacedly embracing the exposed portion of the punch 82. The inner periphery of this stripper 84 is so dimensioned that the lower piston rod 74 is axially slidable through the stripper 84. The piston plunger 73, the lower piston rod 74, the punch 82 and the die 16 are arranged in coaxial alignment.

The main handle 4 has a longitudinal through-hole 41 which merges into an enlarged chamber 41a near the junction between the main handle 4 and the main frame 1 as is clearly shown in FIG. 4. A pipe 42 is inserted into the through-hole 41 while occupying the upper half of the latter. At the inner end portion the pipe 42 is externally threaded for threadedly engaging the upper flange part 21 of the cap 2, the center hole 44 of the pipe 42 communicates with the pressure fluid passage 24 formed in the upper flange part 21 of cap 2 and two sets of set screws 43 are provided in order to securely fix the main handle 4 to the shoulder of the upper jaw 11 of the main frame 1. The outer end portion of pipe 42 is so shaped as to fit a connection or coupling of a suitable pressure fluid source not shown in the drawing. As shown in more detail in FIG. 7, the outer end of the through hole 41 of the main handle 4 diverges outwardly and a fixing nut 46 is screwed over the outer end portion of the pipe 42 so that its converging side abuts snugly against the outwardly diverging end of the through-hole 41.

At the time of assembly of main handle 4 and its related parts, pipe 42 is inserted into the through-hole 41 of the main handle with its inner-end portion being screwed into the upper flange part 21 of cap 2 and the fixing nut 46 is fastened. Next, set screws 43 are fastened so that the main handle 4 is firmly fixed to main frame 1. In the way above described, the three members, i.e. main handle 4, main frame 1 and cap 2 are firmly combined to each other via pipe 42.

A cavity 18 is formed within upper jaw 11 of main frame 1 as shown in FIGS. 5 and 6 and a piston shifting mechanism 9 is incorporated within the cavity 18, which is closed from the outside by a cover 93. The piston shifting mechanism 9 includes a shifting switch 91 encased within the cavity 18 being carried by the cover 93 (see FIG. 5) and a detection terminal 92 which is partly exposed into the piston chamber 23, while confronting the undersurface of the piston plunger 73, being urged by a compression spring 94 accompanying the same. The bottom end of the detection terminal 92 confronts contact 95 of the shifting switch 91. When the piston plunger 73 approaches the lower end of the piston chamber 23 during its downward stroke, the detection terminal 92 is depressed and its bottom end accordingly pushes down the contact 95 of the shifting switch 91. Upon cancellation of the depression on the detection terminal 92 by the upward movement of the piston plunger 73, the detection terminal 92 is again partly exposed into the piston chamber 23 due to the repulsion by the compression spring 94 and the contact 95 of the shifting switch 91 resumes its free disposition.

A hole 13 is formed through the upper jaw 1 1 of main frame 1 and main handle 4 in order to connect cavity 18 for the piston shifting mechanism 9 to the enlarged chamber 41a in the main handle 4. Electric connections 96 run from the shifting switch 91 to a socket 97 disposed at the free end of the main handle 4 through the above-described hole 19 in the main frame 1 and the lower half of the through hole 41 in the main handle 4. The socket 97 is suited for connection to a suitable electric source (not shown). In combination with the electric connections 96 between the shifting switch 91 and the socket 97, a pair of control switches 47 are arranged near the inner end of the main handle 4 as clearly shown in FIGS. 3 and 4. As shown in FIG. 8, the control switches 47, the shifting switch 91 and the electric connections 96 form a series electric circuit and one of the control switches 47, which is for switching on the machine, is accompanied with a self-maintaining relay.

The hydraulically operated working machine, that is the punching machine in the case of the abovedescribed first embodiment, according to one aspect of the present invention having the above-described structure operates in the following manner.

In order to start the running of the pressured fluid source, one of the control switches 47 is depressed by the operators hand gripping the main handle 4. Upon starting of the running of the pressured fluid source, the pressured fluid, say pressured oil, is admitted into the piston chamber 23 through the center hole 44 of the pipe 42 and the pressured fluid passage 24 of the main frame 1. This admission of the pressured fluid causes a corresponding downward stroke of the piston plunger 73. Because the upper flange 71 cooperatively forms one body with the piston plunger 73 via the upper piston rod 72, the flange 71 moves downwardly following the downward stroke of the piston plunger 73 and the highly elastic retracting element 32 is compressed in between the flange 71 and the upper flange part 21 of the cap 2. The piston plunger 73 undergoes further movement and approaches the lower end of the piston stroke while overcoming the repulsion by the retracting 6 element 32. With this downward stroke of the piston mechanism 7 the punch 82 of the work part advances downwards and, in cooperation with the die 16 held by the lower jaw 12 of the main frame 1, punches a hole in a workpiece placed on the die 16.

The dimension of the machine parts are so designed that the undersurface of the piston plunger 73 depresses the detection terminal 92 of the piston shifting mechanism 9 at the very moment that the punching operation is completed. By this depression, the electric circuit shown in FIG. 8 is opened and this causes shifting of the operation of the pressured fluid source. In other words, the pressured fluid in the piston chamber 23 is discharged therefrom and the repulsion of the compressed retracting element 32 forces the piston plunger 73 to move upwardly. This upward movement of the piston plunger 73 automatically cancels the depression on the detection terminal 92 of the piston shifting mechanism 9 and the detection terminal 92 resumes its initial disposition being urged by the compression spring 94'. With a prescribed time delay, i.e. when the piston plunger 73 comes to the end of its upward stroke, the shifting switch 91, now free of the depression by the detection terminal 12, is closed and the electric circuit in FIG. 8 is closed thereby. This closing of the electric circuit induces restarting of the running of the pressured fluid source, the pressured fluid is admitted into the piston chamber 23 and the piston mechanism 9 repeats its reciprocal upward and downward strokes in order to carry out the successive punching operations.

In the case of the above-described embodiment, the urethane retracting element 32 is divided into two pieces by the separator plate 77 disposed to the middle portion of the upper piston rod 72. However, the retracting element 32 can also be in the form of a single piece such as shown in FIG. 9.

The second embodiment of the present invention is shown in FIGS. 10 through 13, in which parts substantially similar to those of the first embodiment in their structures and functions are designated with common reference numerals. In the case of this embodiment, the structures of the main frame 1, the cap 2, the main handle 4, the auxiliary handle 6, the piston mechanism 7, the work part 8 and the piston shifting mechanism 9 are substantially similar to those of the first embodiment. That is, this second embodiment is different from the first embodiment in the structure of the piston retracting mechanism 3.

Similar to the case in the first embodiment, the piston retracting mechanism 3 is confined within the hollow cover 31 fixed on the upper side of the cap 2 and an upper piston rod 72, which is upwardly integral of the piston plunger 73, and extends into the hollow of the cover 31. A guide cylinder is placed on the uppersurface of the cap 2 being concentrically and freely inserted over the upper piston rod 72. As shown in FIG. 11, this guide cylinder 130 is provided with a plurality of upper projections 131 extending from its upper edge and the projections 131 define cut-outs 132 between them. The guide cylinder 130 is further provided with a bottom flange 133 of a somewhat larger diameter. In actual use, the guide 130 is preferably provided with six sets of upper projections 131 in order to adequately maintain the coaxial alignment of the later described washer springs.

A member 134 is fixed to the top of the upper piston rod 72 by a fixing nut 135 while being received within 7 a space defined by the upper projections 131 of the guide cylinder 130 and its upper end flange 136 has a diameter larger than the outer diameter of the guide cylinder 130, more exactly larger than the outer diameter of the circle defined by the outer peripheries of the upper projections 131 of the guide cylinder 130. This upper end flange 136 of member 134 is provided, on its peripheral edge, with a plurality of cut-outs 137. The number of cut-outs 137 of the upper end flange 136 corresponds to that of the upper projections 131 of the guide cylinder 130 and, in the assembled disposition, the' upper projections 131 are in a slidable engagement with the peripheral cut-outs 137 as shown in FIG. 12.

A plurality of washer springs 138 are inserted over the guide cylinder 130 and its upper projections 131 with the lowermost one in abutment with the shoulder of the bottom flange 133 of the guide cylinder 130 and the uppermost one in abutment with the underside shoulder of the upper end flange 136 of member 134.

The hydraulically operated working machine of the above-described second embodiment of the present invention operates in the following manner, operations similar to those described in connection with the foregoing first embodiment being omitted in the explanation.

Following the downward movement of the piston plunger 73 in the piston chamber 23, the member 134, which is connected in one body to the piston plunger 73 via the fixing nut 135 and the upper piston rod 72, moves downwardly and compresses the washer springs 138. When the piston plunger 73 completes its downward stroke, the piston retracting mechanism 3 of the present embodiment assumes the disposition shown in FIG. 13, in which the washer springs 138 are compressed into an almost flat disposition.

During this compression, the internal surface contact of the washer springs 138 with the external periphery of the upper projections 131 of the guide cylinder 130 prevents infavourable diametrical slip between the superimposed washer springs 138. in addition, axial turning of the upper piston rod '72 and the piston plunger 73 is effectively prevented by the meshing engagement between the upper projections 131 of the guide cylinder 130 and the peripheral cut-outs 137 of member 134.

After completion of the punching operation, the pressured fluid in the piston chamber 23 is discharged therefrom and the repulsion of the washer springs 138 forces the piston plunger '73 to move upwardly via member 13% and the upper piston rod When the piston plunger 73 completes its upward stroke, the work part retracting mechanism 3 of the present embodiment resumes the disposition shown in FIG. 10.

As is clearly understood from the foregoing explanation, a number of advantages can be resulted from employment of the present invention.

The hydraulically operated working machine of the present invention is firstly characterized by the fact that the piston retracting mechanism is located outside the machine parts confining the piston chamber for the piston plunger. Thanks to these structural characteris tics, maintenance work for replacement of the work part retracting mechanism can be considerably simplitied. in addition, dimension of the piston retracting mechanism can be designed quite freely without regard to that of the machine parts confining the piston chamber. Further, as there is no need to give a large durable structure to the machine parts confining the piston chamber, the working machine as a whole can be of a 8 remarkably light weight and manufacturing accuracy of the machine can be excellently enhanced.

The hydraulically operated working machine of the present invention is secondly characterized by the fact that the piston retracting mechanism is capable of providing a very large repulsion force in spite of its relatively short stroke. Thanks to such a very large repulsion force, holes can be punched through workpieces while leaving minimized clearances and this leads to the remarkably improved accuracy of the punched hole sizes and the considerably lowered sharp uncomfortable noises during the punching operation. Further, shortness in the necessary stroke enables the piston retracting mechanism to be structured very compactly. The strong and durable repulsion of the retracting element, i.e. the urethane piece(s) in the first embodiment and the washer springs in the second embodiment. can withstand long use even under severe operational conditions.

The hydraulically operated working machine of the present invention is thirdly characterized by the fact that the mechanism for admission and discharge of the pressured fluid into and out of the piston chamber is completely incorporated within the cap and the main handle. This makes the handling and transportation of the machine very simple and convenient. Absence of connecting tubes or like members outside the main body of the machine simplifies and improves the design of the machine.

The hydraulically operated working machine of the present invention is further characterized by the fact that all the elements composing the electric circuit are incorporated within the main frame and the main handle and the control switches are located near the root end of the main handle. This gives simplicity and convenience in the handling and transportation of the machine in the actual use. Operation of the machine can be very easily controlled by using fingers of the operators hand gripping the main handle. In addition, as the relatively fragile piston shifting mechanism is placed within the main frame being attached to the inside face of the cover, the same is well be protected from external shock and the replacement of same can be carried out very simply.

What is claimed is:

1. A hydraulically operated working machine usable for punching and cutting operations and the like comprising, in combination:

a main frame having an interior piston chamber reducing to a narrow opening suited for guiding piston reciprocation;

a cap mounted upon the side of said main frame opposite said opening and arranged so as to close one end of said piston chamber;

a main operating handle joined to said main frame and aligned transverse to the longitudinal axis of the piston chamber, said handle being provided with an internal conduit for connecting said piston chamber to a supply source of pressured fluid for moving the piston assembly in a first direction;

a piston mechanism comprising a piston member mounted for reciprocal movement within said piston chamber and provided on one side with a first extension which extends in said first direction through said main frame and into said opening;

a work head mounted at the free end of said first extension for reciprocating engagement with the workpiece adjacent said opening, said piston mem- 9 ber being further provided with a second extension which extends in a second direction opposite said first direction through said piston chamber and said cap;

a holding member mounted upon the free end of said second extension; and

resilient piston retracting means arranged on the exterior side of said cap and positioned between said holding member and said cap for urging said piston mechanism in said second direction.

2. Hydraulically operated working machine as claimed in claim 1 further comprising a piston shifting mechanism incorporated within said main frame and main handle and having a detection terminal partially extending into said piston chamber in an arrangement to be depressed by said piston mechanism when moving in said first direction.

3. Hydraulically operated working machine as claimed in claim 2 further comprising a cavity formed in said main frame; said piston shifting mechanism further including a shifting switch positioned within said cavity and having a movable contact operated by said detection terminal; means for resiliently biasing said detection terminal in said second direction; a socket positioned at the free end of said handle; means extending through said main frame and said handle for electrically connecting said shifting switch to said socket; and a pair of control switches arranged on said handle near 10 said frame and being connected in electrical series with said shifting switch and said socket.

4. Hydraulically operated working machine as claimed in claim 1 in which said piston retracting mechanism comprises at least one high power piston retracting elements placed on said cap and surrounding said second extension, said holding member comprising a flange-shaped member fixed to the free end of said second extension in such an arrangement as to compress and retracting element between said holding member and said cap upon movement of said piston mechanism in said first direction.

5. Hydraulically operated working machine as claimed in claim 4 in which said high power retracting element comprises a cylindrical shaped urethane body.

6. Hydraulically operated working machine as claimed in claim 4 in which said high power piston retracting element comprises washer springs superimposed upon eaeh other.

7. Hydraulically operated working machine as claimed in claim 6 in which said piston retracting mechanism further comprises a guide cylinder placed on said cap and surrounding said second extension and having at least two upwardly extending projections which are in meshing engagement with peripheral cutouts formed in said flange-shaped member, said washer springs being inserted over said guide cylinder and its upper projections. 

1. A hydraulically operated working machine usable for punching and cutting operations and the like comprising, in combination: a main frame having an interior piston chamber reducing to a narrow opening suited for guiding piston reciprocation; a cap mounted upon the side of said main frame opposite said opening and arranged so as to close one end of sAid piston chamber; a main operating handle joined to said main frame and aligned transverse to the longitudinal axis of the piston chamber, said handle being provided with an internal conduit for connecting said piston chamber to a supply source of pressured fluid for moving the piston assembly in a first direction; a piston mechanism comprising a piston member mounted for reciprocal movement within said piston chamber and provided on one side with a first extension which extends in said first direction through said main frame and into said opening; a work head mounted at the free end of said first extension for reciprocating engagement with the workpiece adjacent said opening, said piston member being further provided with a second extension which extends in a second direction opposite said first direction through said piston chamber and said cap; a holding member mounted upon the free end of said second extension; and resilient piston retracting means arranged on the exterior side of said cap and positioned between said holding member and said cap for urging said piston mechanism in said second direction.
 2. Hydraulically operated working machine as claimed in claim 1 further comprising a piston shifting mechanism incorporated within said main frame and main handle and having a detection terminal partially extending into said piston chamber in an arrangement to be depressed by said piston mechanism when moving in said first direction.
 3. Hydraulically operated working machine as claimed in claim 2 further comprising a cavity formed in said main frame; said piston shifting mechanism further including a shifting switch positioned within said cavity and having a movable contact operated by said detection terminal; means for resiliently biasing said detection terminal in said second direction; a socket positioned at the free end of said handle; means extending through said main frame and said handle for electrically connecting said shifting switch to said socket; and a pair of control switches arranged on said handle near said frame and being connected in electrical series with said shifting switch and said socket.
 4. Hydraulically operated working machine as claimed in claim 1 in which said piston retracting mechanism comprises at least one high power piston retracting elements placed on said cap and surrounding said second extension, said holding member comprising a flange-shaped member fixed to the free end of said second extension in such an arrangement as to compress and retracting element between said holding member and said cap upon movement of said piston mechanism in said first direction.
 5. Hydraulically operated working machine as claimed in claim 4 in which said high power retracting element comprises a cylindrical shaped urethane body.
 6. Hydraulically operated working machine as claimed in claim 4 in which said high power piston retracting element comprises washer springs superimposed upon each other.
 7. Hydraulically operated working machine as claimed in claim 6 in which said piston retracting mechanism further comprises a guide cylinder placed on said cap and surrounding said second extension and having at least two upwardly extending projections which are in meshing engagement with peripheral cut-outs formed in said flange-shaped member, said washer springs being inserted over said guide cylinder and its upper projections. 